1. Field of the Invention
This invention relates to a fine silica particles treated with a silane, and more particularly to a fine silica particles having a high dispersibility and low aggregative properties, a process for their production, and an organic resin composition containing such fine silica particles.
2. Description of the Prior Art
As methods for the surface treatment of silica with silane, commonly available methods are those in which silane is made to adhere to silica particle surfaces by treatment with silicone oil and those in which silane is chemically bonded to silica particle surfaces by treatment with hexamethydisilazane.
Properties required in organic resins, in particular, organic resin films, include transparency, blocking resistance, slip properties, scratch resistance and so forth. Adding spherical fine silica particles in organic resin films is proposed and is reported to bring about an improvement in transparency of the resultant film (Japanese Pre-examination Patent Publication (Kokai) No. 4-348147).
The silica obtained by such surface treatment can be made hydrophobic appropriately, but reactive groups such as silanol groups or alkoxyl groups remaining on the silica particle surfaces may make the silica unable to be dispersed in organic solvents of various types, or may make it highly aggregative. Accordingly, it has been sought to provide fine silica particles having a high dispersibility and low aggregative properties.
Japanese Pre-examination Patent Publication (Kokai) No. 2-160613 discloses fine silica particles having a superior dispersibility, which, however, have a problem that any heating for evaporating solvents may result in a poor primary-particle retention.
When the spherical fine silica particles disclosed in Japanese Pre-examination Patent Publication (Kokai) No. 4-348147 are compounded as a component of a heat-curable or ultra-violet-curable resin composition which is liquid in a relatively low viscosity, the fine silica particles can be dispersed with difficulty in various resins and solvents because they are inorganic matter and hence have so large a specific gravity (larger than 2.0) that they may have a great difference in specific gravity from other materials (components) of the composition, and also because the fine silica particles tend to aggregate on account of the polarity or hydrogen bond of the silanol groups they have. Thus, they have a disadvantage of sedimentation with time during the storage of the composition.